400 SBC: Where is my torque?? - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 12-29-2007, 04:47 AM
Registered User
 
Last photo:
Join Date: Feb 2006
Location: Chicago Area
Posts: 94
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
400 SBC: Where is my torque??

I currently have a 69' Corvette coupe with a 409 (400 + .040) small block, M-20 Muncie and 3.70 axle. This car has no power options- Manual steering, brakes etc.
I finished rebuilding a motor last winter with these specs:

1972 400 SBC, 4-bolt main
Bored .040 w/forged L2352F Speed Pro pistons (14cc Dish)
Block decked just to true-up the surface (not ‘zero decked’)
Stock crank and 5.565 rods
GMPP # 25534431, large port Bow-Tie Vortec (cast iron) heads right out of the box.
(65cc chambers, 2.00 intake, 1.55 exhaust, 206cc intake, 77cc exhaust, LT4 style valve springs, stamped 1.5 rockers w/guide plates)
With the pistons and heads, I figure around 10.25:1 CR.
Lazer Cams mechanical flat tappet cam.
(Part #CS-S281E-286B-08, Duration @ .050 243/248, Lift .511/.480, Lash .026/.028 LS 108, Intake Centerline 104)
Professional Products dual plane aluminum intake (the only Vortec manifold that would fit under my stock small block hood/air cleaner) with a Holley 800 CFM Spread bore double pumper carb.
Stock distributor (recurved) with Pertronix II module and coil
Z-28 oil pan, windage tray and oil pump
Exhaust is full factory 2.5” duals and mufflers with 2.5” ‘Fuelie’ Ram Horn manifolds ported to match the Vortec heads.

I got all this together, fired it up (used EOS lube and broke in cam at 2000 RPM etc) and except for some initial rocker arm to valve cover issues, the motor runs and idles pretty good.
My only complaint is that I don’t seem to have the low-end grunt (torque) that I was expecting from a 400. Am I just being unrealistic?
I would have thought this combo would have given me enough low-end torque to light up the tires from a rolling start in 1st gear (2.52 first gear on the M-20) with the 3.70 axle.
This is a fairly light car and I’m running P255 60R15 street tires- Am I just expecting too much from this combo?
The car pulls real strong once it gets going and winds up to 5500RPM in a big hurry but I REALLY long for that low end torque I was expecting by replacing the ZZ3 with a 400 SBC. This is just a street car to play with in the summer months so I haven’t gone to the track to see what it runs or had any dyno pulls done with the car.

Any suggestions?
Is my cam wrong for my application (I did choose it mainly for the cool idle quality and I wanted a solid cam in this motor)?
Are the heads too big?
Any advice would be greatly appreciated.
Thanks!
Elm

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 12-29-2007, 05:08 AM
Registered User
 
Last photo:
Join Date: Dec 2007
Location: Florida
Posts: 28
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Combo sounds pretty good. If anything, the cam is a little tight (108) for its size in a 400 (hope you don't need power brakes).
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 12-29-2007, 05:38 AM
dawg's Avatar
NAVY VETERAN
 
Last photo:
Join Date: Aug 2004
Location: Colebrook Connecticut
Age: 55
Posts: 908
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
yeah cam isnt a made for low end torque.
if you got something with a 110 to 114 lobe centerline youll notice a big difference.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 12-29-2007, 06:35 AM
Hotrodders.com Moderator
 

Last journal entry: PICTURE TEST
Last photo:
Join Date: Jan 2004
Location: york pa
Age: 52
Posts: 2,795
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
engine

I figure the static right around 10.0:1.

I did not see any mention of what your initial and total timing is set at???

I need to know that before i make any more recomendations.

Also if you have a compression gage let me know what the cranking compression is.


Keith
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 12-29-2007, 09:00 AM
CNC BLOCKS NE's Avatar
CNC Blocks Northeast
 
Last photo:
Join Date: Sep 2006
Location: NORTHEAST
Age: 54
Posts: 1,429
Wiki Edits: 0

Thanks: 1
Thanked 16 Times in 16 Posts
Quote:
Originally Posted by ezobens

1972 400 SBC, 4-bolt main
Bored .040 w/forged L2352F Speed Pro pistons (14cc Dish)
Block decked just to true-up the surface (not ‘zero decked’)
Stock crank and 5.565 rods
GMPP # 25534431, large port Bow-Tie Vortec (cast iron) heads right out of the box.
(65cc chambers, 2.00 intake, 1.55 exhaust, 206cc intake, 77cc exhaust, LT4 style valve springs, stamped 1.5 rockers w/guide plates)
With the pistons and heads, I figure around 10.25:1 CR.
Lazer Cams mechanical flat tappet cam.
(Part #CS-S281E-286B-08, Duration @ .050 243/248, Lift .511/.480, Lash .026/.028 LS 108, Intake Centerline 104)
Elm
We use a lot of the Big Vortec Bowtie heads on our circle track engines we build and we have seen very very good results.

But to use them in your application I don't think its the head your looking for as the intake runner size that is advertised 206 is is a type O as they are actually 216 to 218 from what we have seen and the new ones they are claiming 225 on the intake runners.

The .050 are small which is good but your ADV. mumbers are 281/286 which is kind of high meaning very slow opening and closing ramps which will hurt your dynamic compression and your low end torque. Do you know what your .200 numbers are on that cam.

Those heads we use we are in the .570 lift area with 1.8 to 1.9 ratio rockers 11:.01 and with a 600 HP carb we are in the 590 to 610 horse range

The smaller runner head might be what your looking for and maybe a cam change on top of that.

The big runner head and low lift is killing your velocity which kills the torque and using the smaller runner head will pick up your air speed ing the port making for better torque.

Hope this has helped, Carl
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 12-29-2007, 09:52 AM
Registered User
 
Last photo:
Join Date: Feb 2006
Location: Chicago Area
Posts: 94
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Thank you for your responses!
I haven't done a static compression check yet (I will in the next few weeks once this snow melts!). Unless there is something way off in that department, even 10:1 static CR should be ideal for this motor?

I'm going off of memory here but I believe the timing is currently set at 8 degrees initial and full advance is 36 degrees at 2700 RPM.
I do know the distributor was re-curved to allow full advance at 2700 RPM and the total advance capability(minus initial) of the distributor itself is 28 degrees.
This is the factory cast iron tach drive points distributor that was rebuilt/recurved utilizing a Pertronix II module and coil for spark.
I am currently not running any vacuum advance(I've tried either way and no significant performance difference).

Hope this helps- Thanks again!
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 12-29-2007, 09:53 AM
CNC BLOCKS NE's Avatar
CNC Blocks Northeast
 
Last photo:
Join Date: Sep 2006
Location: NORTHEAST
Age: 54
Posts: 1,429
Wiki Edits: 0

Thanks: 1
Thanked 16 Times in 16 Posts
I also should have mention these are 358 CID engines with tappet cams and .875 lifter bores and we are using BBC cam tunnels in these blocks.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 12-29-2007, 10:32 AM
Hotrodders.com Moderator
 

Last journal entry: PICTURE TEST
Last photo:
Join Date: Jan 2004
Location: york pa
Age: 52
Posts: 2,795
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
timing

Get you timing to 18 initial, with the vacuum advance un-hooked. And about 36 total. Then hook the vacuum advance to a full port source.

When you get the smile off of your face because you just toasted the tires get back to us.

8 initial is not near enough, plus all the mechanical should be in by 2000


Keith
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 12-29-2007, 10:46 AM
King of my Man-cave.
 
Last photo:
Join Date: Nov 2003
Location: Michigan
Age: 55
Posts: 2,838
Wiki Edits: 0

Thanks: 2
Thanked 4 Times in 2 Posts
Quote:
Originally Posted by CNC BLOCKS N/E
I also should have mention these are 358 CID engines with tappet cams and .875 lifter bores and we are using BBC cam tunnels in these blocks.
Which has what to do with a street 400 SBC??

tom
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 12-29-2007, 11:01 AM
Registered User
 
Last photo:
Join Date: Feb 2006
Location: Chicago Area
Posts: 94
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Keith,
At 18 initial advance, I will max out at 46 degrees at 2700 in my current set-up.
How do I limit the total distributor advance (which is 28 degrees) to only 18 degrees? Do I need to get some sort of limiting bushing for the mechanical advance?

Also, what springs can I use to get my timing all in by 2000 RPM?
I've tested the springs from the Crane re-curve kit (currently using a blue/heavy spring and a silver/med spring) on a distributor machine. If I use the lightest springs to get the timing in at 2000 RPM, I run the risk of having erratic timing at and off idle because the springs would be so weak (I currently have my idle set about 850 rpm) that the timing would be bouncing all over the place. With the lopey idle of the cam, won't this create other issues?

What should the total vacuum advance (degrees) be for this set-up?

Sorry for the 20 questions but distributors have always been a bit of a gray area for me.
Thanks!
Elm
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 12-29-2007, 11:19 AM
Registered User
 
Last photo:
Join Date: Feb 2006
Location: Chicago Area
Posts: 94
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
One more tidbit of info:
I had asked the 'Cam Wizard' at Lazer Cams about the recommended timing for this cam. At the time, he suggested starting with 10 degrees initial with 34-36 degress total at 2800-3000 RPM.
That is why I have my distributor currently set-up the way it is.
Unfortunately, the Cam Wizard is no longer with us so I'm not able to ask him any follow up questions regarding his original recommendation.
Hope this helps-
Thanks!
Elm
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 12-29-2007, 02:04 PM
Member
 
Last photo:
Join Date: Feb 2003
Posts: 642
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I would get a "recurve kit" for the distributor and use one light and one medium spring and a bushing from the kit to limit the mechanical advance to 32-36 degrees. I personally would not even bother with a vac advance with a cam of that nature.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 12-29-2007, 02:24 PM
How fast is fast enough?
 
Last photo:
Join Date: Jun 2005
Location: St. Louis, MO
Age: 29
Posts: 8,691
Wiki Edits: 0

Thanks: 17
Thanked 282 Times in 262 Posts
Not running vacuum advance or EGR (when you can) is stupid. YEs it is for emissions- but it also leads to longer engine life and better part throttle economy. IT HAS NO EFFECT ON WOT PERFORMANCE. It just makes for a happier street engine.

Your heads and cam are not really suited for torque. It'll be a lot of fun on the strip with some steep gears... but lazy on the street. I suggest going with modified stock Vortec castings (maybe some minor port work to clean them up) and a cam with 10* less duration @.050". YOu'll probably loose about 65 HP, but gain a lot of torque. And on the street, "Torque moves cars; horsepower sells cars."
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 12-29-2007, 02:35 PM
CNC BLOCKS NE's Avatar
CNC Blocks Northeast
 
Last photo:
Join Date: Sep 2006
Location: NORTHEAST
Age: 54
Posts: 1,429
Wiki Edits: 0

Thanks: 1
Thanked 16 Times in 16 Posts
Quote:
Originally Posted by machine shop tom
Which has what to do with a street 400 SBC??

tom
Read all my posts and you can easly see where it fits in as I did not add that in my earlier post and I was using this to compare with ezobens engine

Again please read both of my post as its not hard to figur out LOL
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 12-29-2007, 02:39 PM
CNC BLOCKS NE's Avatar
CNC Blocks Northeast
 
Last photo:
Join Date: Sep 2006
Location: NORTHEAST
Age: 54
Posts: 1,429
Wiki Edits: 0

Thanks: 1
Thanked 16 Times in 16 Posts
Quote:
Originally Posted by k-star
Get you timing to 18 initial, with the vacuum advance un-hooked. And about 36 total. Then hook the vacuum advance to a full port source.

When you get the smile off of your face because you just toasted the tires get back to us.

8 initial is not near enough, plus all the mechanical should be in by 2000


Keith
On these fast burn heads we have to only run about 31 to 33 degrees of total timing on the dyno and I would say at 36 degrees would kill the HP and Torque from what we have seen.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
427 sbc out of a 400 camaro409 Engine 23 08-02-2009 09:25 AM
SBC Strokers - 350 vs 400 Blocks & Combos (not just 383 & 406) ez2cdave Engine 11 05-21-2007 09:34 PM
My sbc 400 build up, please review Guitar Charlie Engine 13 06-17-2004 08:06 AM
sbc 400 cam choice camino_man Engine 11 06-07-2004 03:22 AM
400 SBC Balancing and info ? Brobob Engine 8 10-31-2002 03:44 PM


All times are GMT -6. The time now is 10:42 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.